This invention can be used any time a user needs to “see” an otherwise invisible object placed within the setting in which it would normally appear, and in this case, onto a video stream. This form of image “augmentation” is known as augmented reality (AR), and in this case is considered video-based AR since it uses a video camera, as opposed to a see-through setup (as might be done with partial mirrors). A video-based AR setup has only a few basic components, including (1) a camera with a known field of view (FOV), (2) a means to determine and adjust the position and orientation of the camera, and (3) a computer that creates computer-generated virtual objects that correspond to what the camera is seeing by using the previous two components.
Typically, one of the physically largest components is the second one, wherein a tracking system is used to determine the position and orientation of the camera. In many applications of video-based AR, the camera does not need to change location in the environment. In these scenarios, however, it is often desirable for the camera to be able to change orientation such that it can view an environment larger in scope than its field of view. In this case, it is possible for the camera to be placed on a motion platform such that the camera can be aimed by a computer system with the use of actuators (usually motors connected to a gear train). Such cameras and camera motion platforms are often referred to as “pan-tilt-zoom” systems. Such systems permit the camera to remain in a fixed location, but have variable orientation which may be controlled by an external system. This can eliminate the requirement for a large, expensive tracking system to determine the position and orientation of the camera.
Often, in these kinds of applications, it is desirable to have the camera's field of view follow a real or virtual object appearing in the scene as it moves through the environment without requiring human intervention.